1. Field of the Invention
The present invention relates to a track jump apparatus for jumping a position of an actuator to a position corresponding to a target recording track so as to irradiate the target recording track with a laser beam spot to be irradiated to a predetermined recording track on a recording medium via an objective lens of the actuator, the track jump apparatus being used in an information reproducing apparatus, information recording apparatus or information recording/reproducing apparatus using a recording medium such as an optical disk.
2. Description of the Related Art
Conventionally, feed-forward type open control method has been employed for control on track jump in a compact disk (CD) player and the like, in which acceleration pulse of a predetermined amount is applied to an actuator drive at the same time when a jump start instruction is dispatched and deceleration pulse of a predetermined amount is applied to that drive at a desired timing.
However, with current increased density of an optical disk like DVD, as the track pitch is narrowed, the following problem occurs in an open control of a conventional feed forward method. First, because blind zone and a delay of reaction time exist in the driving system and detecting system of the tracking servo, even if a deceleration pulse is applied, sometimes actual driving is delayed or detection of deceleration and servo close timing is delayed. If a sufficient jump time is secured like a case of CD or a so-called capture range which is a range capable of obtaining an effective tracking error signal at the time of lead-in after a servo close is wide, the delay of the driving system or detecting system does not affect stabilization of the tracking servo largely.
However, if the same amount of pulse is used for the acceleration pulse and deceleration pulse like the conventional track jump in case of a narrow track pitch, the jump time decreases. Thus, the aforementioned blind zone and a rate of the delay with respect to the jump time increase so that stabilization of the tracking servo is largely affected. If the track pitch is narrow, the aforementioned capture range is also narrow. As a result, the frequency of overshoot caused at the servo close increases so that it is out of the servo band. Thus, no braking is applied so that the jump fails or it takes long until stabilization is accomplished.
As a method for preventing such a unstable condition of the track jump, a method in which the same amount of pulse is not used for the acceleration pulse and deceleration pulse but after a predetermined amount of the acceleration pulse is applied, an interval between a jump start and zero cross of the tracking error is measured and then the amount of the deceleration pulse is adjusted based on a deviation between a measured zero cross interval and an appropriate zero cross interval, has been proposed.
To measure the zero cross point accurately, some extent of measuring time is required. If the same amount of the acceleration pulse and deceleration pulse is applied when the track pitch is narrow, the jump time becomes shorter than the conventional case, so that a necessary measuring time cannot be obtained. Therefore, the accuracy of the measured zero cross point deteriorates so that a deceleration pulse calculated from the zero cross interval based on this zero cross point becomes not appropriate, thereby further disturbing stabilization of the tracking servo.
Recently, a servo system for digital processing with digital signal processor (DSP) has been developed. In this system, the tracking error signal is sampled upon a track jump and then the output timing of the deceleration pulse and close timing of the tracking servo are determined based on the sampled value, so that a delay of a timing of one sampling at the maximum occurs.
Therefore, if the track pitch is decreased, the jump time becomes shorter, so that the delay of the timing of one sampling affects largely, thereby not only making a unstable jump but also the jump operation not functioning properly sometimes leading to a jump failure.
On the other hand, to prevent an occurrence of a problem due to shortening of the jump time as described above, a method for reducing the acceleration/deceleration amounts can be considered. However, generally if the acceleration pulse and deceleration pulse are decreased, relatively an influence of a disturbance increases. The disturbance is caused by a deflection, a change of slider state, shock or the like and a size of an estimated disturbance is almost determined. Because the track jump method is carried out by open control as described above, basically this is weak against the disturbance. Therefore, even if the acceleration/deceleration amount is decreased in the conventional track jump method, the influence of the disturbance is so strong that the track jump cannot be stabilized.
Thus, a method in which feed back control is carried out even during a track jump by feed forward control to achieve a stabilized jump with some extent of jump time secured has been proposed (Japanese Patent Application Laid-Open No. HEI 9-167357). According to this method, even if the disturbance such as a deflection of disk occurs, a stabilized tracking servo lead-in is possible after the track jump ends.
However, although according to the method disclosed in the aforementioned Patent Application, a trajectory of a beam position at a jump time needs to be provided as an object value for feed back control, because feed forward control of applying a deceleration pulse just after the acceleration pulse ends is carried out, the trajectory of the aforementioned beam position becomes a shape like quadratic curves are combined. As a result, because the object value itself is high in view of band, an effect of the feed back control cannot be expected so high. That is, because according to this method, the constant deviation is relatively large, it is difficult to stabilize the tracking servo in a short time.
Accordingly, the present invention has been achieved in views of these problems, and therefore, it is an object of the invention to provide a track jump apparatus capable of achieving a stabilized track jump with some extent of jump time secured even if the track pitch is narrow and further stabilizing the tracking servo in a short time.
A track jump apparatus in accordance with the present invention is an apparatus for making an actuator jump in order to move a spot position of a laser beam emitted through an objective lens of the actuator from a current position to an object position corresponding to a desired recording track on a recording medium. The track jump apparatus includes: an actuator driving device that moves the actuator in accordance with a driving signal; a tracking error signal detecting device that detects a tracking error signal on the basis of a change of return light from the recording medium caused by a change of the spot position of the laser beam relative to the recording track; a feed-forward control device that applies an acceleration pulse and a deceleration pulse to the actuator driving device; and a position control device that controls a position of the actuator using a feedback of the driving signal so as to reduce a difference between an object value and the tracking error signal detected by the tracking error signal detecting device, when making the actuator jump in order to move the spot position of the laser beam from the current position to the object position. The feed-forward control device sets a constant speed period during which neither of the acceleration pulse and the deceleration pulse is applied to the actuator driving device between an acceleration period during which the acceleration pulse is applied to the actuator driving device and a deceleration period during which the deceleration pulse is applied to the actuator driving device.
In the track jump apparatus in accordance with the present invention, when receiving an instruction of the track jump, the feed-forward control device applies the acceleration pulse to the actuator driving device. By driving the actuator driving device according to the acceleration pulse, the spot position of the laser beam is moved, thereby changing the spot position relative to the recording track. As the spot position relative to the recording track is changed, the return light obtained from the recording medium is also changed. The changes of the return light are detected as the tracking error signal by the tracking error signal detecting device. The position control device compares the tracking error signal with the object value, and controls the position of the actuator using the feedback of the driving signal so as to reduce a difference between the tracking error signal and the object value.
After applying the acceleration pulse to the actuator driving device, the feed-forward control device stops applying the acceleration pulse, and maintains the non-pulse state that neither of the acceleration pulse and the deceleration pulse is applied to the actuator driving device during a predetermined period. This period is the constant speed period. If the feedback control is carried out by the position control device within the constant speed period, the frequency band in the feedback control is substantially lowered, so that the stable servo loop is formed. As a result, the position of the actuator can be moved to the object position in a stable manner.
When decelerating the actuator, the feed-forward control device applies the deceleration pulse to the actuator driving device. As a result, the actuator reaches the object position, so that the spot position of the laser light accurately matches the object position.
Thus, appropriate feedback control about the position of the actuator is carried out, so that with some extent of jump time secured even for a disk having a narrow pitch, accurate, stabilized track jump can be achieved.
In the aforementioned track jump apparatus in accordance with the present invention, to obtain the effect of the feedback control more efficiently, the constant speed period may be longer than the acceleration period and may be longer than the deceleration period.
In the aforementioned track jump apparatus in accordance with the present invention, the feed-forward control device may execute application of the acceleration pulse, and then execute a non-pulse operation that application of the acceleration pulse and application of the deceleration pulse are suspended during a predetermined period, and then execute application of the deceleration pulse. Thus, by performing the non-pulse operation between the application of the acceleration pulse and the application of the deceleration pulse, the effect of the feedback control can be obtained more efficiently even if the pitch between the recording tracks is small.
In the aforementioned track jump apparatus in accordance with the present invention, the feed-forward control device may execute application of the acceleration pulse, and then execute a non-pulse operation that application of the acceleration pulse and application of the deceleration pulse are suspended during a predetermined period, and then execute application of the deceleration pulse, and then alternately repeat the non-pulse operation and the application of the deceleration pulse in this order. Thus, since the deceleration pulse is intermittently applied, the speed of the movement of the actuator is gradually reduced after the actuator is quickly moved near the object position, and finally, the actuator reaches the desired recording track accurately. As a result, the lead-in of the tracking servo can be ended in a short time.
In the aforementioned track jump apparatus in accordance with the present invention, the feed-forward control device may execute application of the acceleration pulse, and then execute a non-pulse operation that application of the acceleration pulse and application of the deceleration pulse are suspended during a predetermined period, and then alternately repeat application of the acceleration pulse and the non-pulse operation in this order, and then execute application of the deceleration pulse. Thus, since the acceleration pulse is intermittently applied, the speed of the movement of the actuator is gradually increased when the track jump is started, the influence of the eccentricity of the recording medium can be removed.
In the aforementioned track jump apparatus in accordance with the present invention, the feed-forward control device may has a plurality of application patterns of the acceleration pulse and a plurality of application patterns of the deceleration pulse, and select one of the plurality of application patterns of the acceleration pulse and one of the plurality of application patterns of the deceleration pulse depending on a distance that the actuator jumps. For example, if the distance between the current position and the object position is short, it is appropriate that the application of the acceleration pulse is carried out once, and next, the non-pulse operation is carried out once, and next, the application of the deceleration pulse is carried out once. On the other hand, if the distance between the current position and the object position is long, it is appropriate to carry out the intermittent application of the acceleration pulse or the intermittent application of the deceleration pulse. Thus, the appropriate application pattern is different depending on the distance between the current position and the object position. In consideration of this fact, the feed-forward control device may select one of the plurality of application patterns of the acceleration pulse and one of the plurality of application patterns of the deceleration pulse depending on the distance between the current position and the object position, namely, depending on the distance that the actuator jumps.
In the aforementioned track jump apparatus in accordance with the present invention, the feed-forward control device may include: a profile setting device that sets a profile which represents a change of a position of the actuator as time passes; and a feed-forward compensation device that includes a second order differentiator and that uses the profile set by the profile setting device as an internal object value. The profile includes a acceleration part representing the change of the position of the actuator when a movement of the actuator is accelerated, a constant speed part representing the change of the position of the actuator when a speed of the movement of the actuator is constant, and a deceleration part representing the change of the position of the actuator when the movement of the actuator is decelerated. The constant speed part is located between the acceleration part and the deceleration part. The feed-forward compensation device carries out a second order differential to the profile to apply the acceleration pulse and the deceleration pulse.
The profile setting device sets the profile. The profile is supplied to the feed-forward compensation device. The feed-forward compensation device then carries out the second order differential to the supplied profile. As a result, the feed-forward output is obtained from the feed-forward compensation device. Since the constant speed part is placed between the acceleration part and the deceleration part in the profile, the feed-forward output that the constant speed period is placed between the acceleration pulse and the deceleration pulse is obtained. Then, the feed-forward output is supplied to the actuator driving device. Thus, the feed-forward control and the feedback control is efficiently carried out, so that the accurate track jump can be carried out. Furthermore, since the waveform of the profile can be easily changed or easily replaced with another, the movement pattern of the actuator can be easily changed by changing or replacing the waveform of the profile.
To the aforementioned track jump apparatus in accordance with the present invention, a linearization conversion device that carries out a linearization conversion to the tracking error signal may be added. In this case, the position control device uses the profile as the object value, and controls the driving signal so as to reduce a difference between an output value obtained from the linearization conversion device and the object value.
The tracking error signal obtained from the tracking error signal detecting device is a non-linear signal. The linearization conversion device converts this non-linear tracking error signal into the linear tracking error signal. Then, the position control device uses the profile as the object value, and controls the driving signal so as to reduce a difference between the linear tracking error signal and the profile. The profile includes the constant speed part between the acceleration part and the deceleration part. Therefore, the feedback control is carried out on the basis of the comparison between the profile including the constant speed part and the linear tracking error signal. Accordingly, the substantial frequency band in the feedback control is lowered, so that the stable servo loop is formed. As a result, the position of the actuator matches the object position accurately after the track jump, and the lead-in of the tracking servo is ended in a short time.
To the aforementioned track jump apparatus in accordance with the present invention, a determining device that determines at least whether a value of the tracking error signal increases or decreases may be added. In this case, the linearization conversion device includes a first conversion table used when the value of the tracking error signal increases and a second conversion table used when the value of the tracking error signal decreases, and the linearization conversion device selects one of the first conversion table and the second conversion table depending on whether the tracking error signal increases or decreases. By selecting the conversion table depending on whether the non-linear tracking error signal increases or decreases, the appropriate conversion table can be used in the linearization conversion process. Therefore, the accurate linear tracking error signal can be generated.
To the aforementioned track jump apparatus in accordance with the present invention, a first determining device that determines at least whether a value of the tracking error signal increases or decreases may be added. In addition to this, a second determining device that determines a detection method of the tracking error signal may be added. In this case, the linearization conversion device includes a plurality of first conversion tables used when the value of the tracking error signal increases and a plurality of second conversion tables used when the value of the tracking error signal decreases, and the linearization conversion device selects a conversion table from among the plurality of first conversion tables and the plurality of second conversion tables depending on the detection method and depending on whether the tracking error signal increases or decreases. There is a case where the detection method of the tracking error signal differs depending on the type of the recording medium. In consideration of this fact, the second determining device determines the detection method, and the linearization conversion device selects the conversion table suitable for the detection method. Therefore, if the detection method of the tracking error signal differs, the non-linear tracking error signal can be always converted into the appropriate linear tracking error signal.
In the aforementioned track jump apparatus in accordance with the present invention, the determining device may further determine whether the value of the tracking error signal is a positive value or a negative value, when determining that the value of the tracking error signal increases. When the value of the tracking error signal increases, the information indicating whether the value of the tracking error signal is positive or negative is needed to efficiently carry out the linearization conversion. This determining device provides this information.
In the aforementioned track jump apparatus in accordance with the present invention, the determining device may detect a timing at which the value of the tracking error signal reaches a peak value of the tracking error signal, and determine on the basis of the detected timing whether the value of the tracking error signal increases or decreases. The direction of the change of the value of the tracking error signal changes from increase to decrease at the timing at which the value of the tracking error signal reaches its peak. Therefore, the determining device can easily determine on the basis of the detected timing whether the value of the tracking error signal increases or decreases.
In the aforementioned track jump apparatus in accordance with the present invention, the determining device may detect a total amount of the return light obtained from the recording medium, and determine on the basis of the detected total amount whether the value of the tracking error signal increases or decreases.
In the aforementioned track jump apparatus in accordance with the present invention, in a case where the recording track corresponding to the current position and the recording track corresponding to the object position are adjacent to each other, the profile including the acceleration part, the constant speed part and the deceleration part may be used. Since the constant speed part is placed between the acceleration part and the deceleration part, the substantial frequency band in the feedback control can be lowered, so that the effective feedback control can be carried out within the constant speed period. Accordingly, the stability and accuracy of the movement of the actuator is increased.
In the aforementioned track jump apparatus in accordance with the present invention, in a case where there is one or more than one recording track between the recording track corresponding to the current position and the recording track corresponding to the object position, the profile including the acceleration part, the constant speed part and the deceleration part may be used, and the object value and the output value obtained from the linearization conversion device may be replaced with initial values at a timing that the spot position of the laser beam matches an on-track position of the recording track when the spot position traverses the recording track. In addition, the initial values are values used as the object value and the output value when the actuator starts to jump.
In the waveform of the tracking error signal, the zero cross point appears each time the spot position coincides with the on-track position of the recording track when the spot position traverses the recording track. In consideration of this fact, the object value and the linear tracking error signal are replaced with their initial values at the timing that the spot position of the laser beam matches the on-track position of the recording track. In the case where the profile is used as the object value, the profile is created in such a way that the object value is initialized at the timing that the spot position matches the on-track position. Since the initialization of the object value and the linear tracking error signal is repeated during the track jump, the similar operation to the repetition of the single track jump is performed during the long track jump. Therefore, the effective feedback control is repeatedly carried out, so that the stability and accuracy of the track jump can be increased.
In order to improve the stability and accuracy of the track jump, it is preferable that the object value and the output value are replaced with the initial values each time the spot position of the laser beam traverses the recording track. Alternatively, the object value and the output value may be replaced with the initial values when the spot position of the laser beam traverses a predetermined number of the recording tracks. In this case, the track jump period can be shortened.
Furthermore, the object value and the linear tracking error signal may be replaced with the initial values at the timing that the spot position of the laser beam matches the middle position of the recording tracks adjacent to each other.
To the aforementioned track jump apparatus in accordance with the present invention, a speed control device that controls a speed of a movement of the actuator using the feedback of the driving signal so as to reduce a difference between a zero cross frequency of the tracking error signal and an object frequency may be added. By reducing the difference between the zero cross frequency of the tracking error signal and the object frequency, the track jump period can be shortened. By the combination of the speed control device and the position control device, the stability and accuracy of the track jump can be increased and the quick track jump can be achieved.
To achieve the stabile, accurate and quick track jump, a balance of the control of the speed control device and the control of the position control device is important. To balance the two controls, it is determined whether or not the control of the speed control device is carried out, depending on the number of the recording tracks between the recording track corresponding to the current position and the recording track corresponding to the object position. For example, when a number of the recording tracks between the recording track corresponding to the current position and the recording track corresponding to the object position is not greater than a predetermined number, only the control of the position of the actuator with the position control device is carried out. When the number of the recording tracks between the recording track corresponding to the current position and the recording track corresponding to the object position is greater than the predetermined number, both the control of the speed of the movement of the actuator with the speed control device and the control of the position of the actuator with the position control device are carried out.
Moreover, in order to achieve the quick track jump, it is preferable to make the speed of the movement of the actuator when the control of the speed control device is carried out faster the speed of the movement of the actuator when a control of the position control device is carried out.
Moreover, in order to achieve the stable, accurate and quick track jump, the control of the speed of the movement of the actuator with the speed control device may be carried out during the constant speed period, and the control of the position of the actuator with the position control device may be carried out during the deceleration period or until the spot position of the laser beam matches the on-track position corresponding to the object position after the deceleration of the movement of the actuator is finished.
To the aforementioned track jump apparatus in accordance with the present invention, a tracking servo control device that controls the position of the actuator using the feedback of the driving signal so as to set a value of the tracking error signal at zero after a jump of the actuator is finished may be added. And, the speed control device may include a first phase compensation device, the position control device may include a second phase compensation device, and the tracking servo control device may include a third phase compensation device.
The tracking servo control device controls the position of the actuator so as to set the value of the tracking error signal at zero after the jump of the actuator is finished. Furthermore, each of the speed control device, the position control device and the tracking servo control device includes a phase compensation device suitable for the property of each control device. Therefore, the controls of the respective control devices are appropriately carried out in different frequency bands.
In the aforementioned track jump apparatus in accordance with the present invention, the second phase compensation device may receive an integration term of the first phase compensation device when shifting from a control of the speed control device to a control of the position control device, and the third phase compensation device may receive an integration term of the second phase compensation device when shifting from the control of the position control device to a control of the tracking servo control device. Thus, if the actuator that jumps under the influence of an inertial system is affected by a spring system when the actuator reaches the object position, the spot position of the laser beam is quickly positioned on the object position, because it is possible to reduce low frequency components of the integration term by providing the integration term of the low frequency components from the former control device to the later control device.
Moreover, in the aforementioned track jump apparatus in accordance with the present invention, the position control device may receive an integration term of a drive amount from the speed control device when shifting from a control of the speed control device to a control of the position control device, and the tracking servo control device may receive the integration term of the drive amount from the position control device when shifting from the control of the position control device to a control of the tracking servo control device. Thus, if the actuator that jumps under the influence of an inertial system is affected by a spring system when the actuator reaches the object position, the spot position of the laser beam is quickly positioned on the object position, because it is possible to control in accordance with the drive amount so as to remove the influence of the spring system by providing the integration term of the drive amount from the former control device to the later control device.
In the aforementioned track jump apparatus in accordance with the present invention, the position control device may receive information representing a number of the recording tracks that the actuator jumps from the speed control device when shifting from a control of the speed control device to a control of the position control device, and the tracking servo control device may receive the information representing the number of the recording tracks that the actuator jumps from the position control device when shifting from the control of the position control device to a control of the tracking servo control device. The displacement of the actuator can be determined on the basis of the information representing the number of the recording tracks that the actuator jumps. Thus, if the actuator that jumps under the influence of an inertial system is affected by a spring system when the actuator reaches the object position, the spot position of the laser beam is quickly positioned on the object position, because it is possible to reduce the displacement amount of the actuator by providing the information representing the number of the recording tracks that the actuator jumps from the former control device to the later control device.
In the aforementioned track jump apparatus in accordance with the present invention, in a case where a control of the speed control device, a control of the position control device and a control of the tracking servo control device are sequentially carried out, an integration term used in a previous control or an integrated drive amount is added as an offset in a feed-forward manner during the control of the position control device or during an open control period during which acceleration or deceleration of a movement of the actuator is executed under a feed-forward control. Thus, if the actuator that jumps under the influence of an inertial system is affected by a spring system when the actuator reaches the object position, the spot position of the laser beam is quickly positioned on the object position, because it is possible to control so as to remove the influence of the spring system by the feed-forward addition of the drive amount.
In the aforementioned track jump apparatus in accordance with the present invention, in a case where the recording medium has a land track and a groove track and information is recorded onto the land track and the groove track, the position control device uses a half wave of the tracking error signal to move the spot position of the laser beam from the land track to the groove track or from the groove track to the land track. Thus, the accurate track jump can be achieved with respect to the recording medium that information is recorded onto both the land track and the groove track.
To reduce the influence of the eccentricity of the recording medium more efficiently, a gain control device that adjusts a gain of the tracking error signal and an offset control device that adjusts an offset of the tracking error signal may be added to the aforementioned track jump apparatus in accordance with the present invention.
The nature, utility, and further feature of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.